Mori did write the file on her computer, or rather Future Mori did. The chapter on the Third Breaking established that time travel is possible, but can’t go back further than the birth of Anon. I suspect Mori is about to time travel in order to buy time to prepare to save her friends. Either we were just shown what happened in the original timeline, or Future Mori did something to save Sarin while making it look like the assassination attempt succeeded. My money is on showing up to knock out the shooter and hitting Sarin with a teleportation device instead, giving a good reason to depict the shooter as a shadowy figure (unless the shooter really looks like that because who knows in this world?)

Future Mori might even be the inhabitant of the house in the bubble. If the field slows down time enough, going back to before it was put in place and waiting for the field to break could be the fastest way to intervene (or just the simplest use of time travel). Future Mori’s warning might even have been transmitted from the bubble when it went down so she’d only have to travel in time once.

In any case, Page 4 was definitely the start of Mori’s attempts to save everyone. The rest of the chapter has been a “flashback” to the things she’s trying to stop.

Wait! I changed my mind. Replacing the shooter would be obvious to the shooter, and if the shooter doesn’t come back it would be obvious to whoever sent them. There’s probably some duplication shenanigans going on. That, or Mori saved Sarin by pulling her into the time-travel spell and they both live in the house in the bubble.

We’re clearly looking at some form of time travel / prediction magic at work in this story-line, there’s no other way this makes sense.

So yeah, I figure we have… 3 bad ends that need tied up?

Pricilla appeared to be mind controlled by “Steve” into / has snapped and decided to start stabbing Kili / Herself
The time crew is about to be killed by an Eternity Bomb
Sarin just got zapped into oblivion

I suspect Mori is being warned about this somehow from the spirit world, or by some form of time travel shinanigans.